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OM20 Universal Outdoor Modem
4.6 Clocking Options
The modem supports a number of different clocking options that can be recovered from
the satellite or the terrestrial links. The various clocking options allow users to determine
which clock will best fit their applications. Figure 4-7 gives an overview on how the
modem processes the various clocks for the Tx Clock source and the Rx Buffer Clock
source. Tx and Rx Clocks may be independently locked.
J 3
SD
TT
ST
High Stability
Oscillator
TRANSMIT
RECEIVE
CLOCK
RECOVERY
NORMAL
INVERTED
J 3
RT
BUFFER CLK POL
RD
DATA POLARITY
4.6.1 TX Clock Options
TX clock options can be recovered from the terrestrial interface, satellite interface or internally
generated. The allows users to select SCTE Clock (Terrestrial) or the SCT internal clock. The
modem also allows user to recover the SCT Clock from the satellite (SCR) or from the modem
internally. The modem allows users to select clock polarity. The Tx clock selections available
are:
TM116 – Rev. 1.2
SCTE
SCT
HIGH STABILITY
INTERNAL
REF FREQ
SRC
SCT CLK
SRC
SCR
IDI
SCT
BUFFER CLK
SRC
SCTE
RX SAT
INVERT NONE
INV . TERR & BASE
INV . BASEBAND
INV . TERR DATA
Figure 4-7. Clocking and Polarity Diagram
INVERT NONE
INV . TERR &BASE
INV . BASEBAND
INV . TERR DATA
DATA POLARITY
CLOCK &
DATA
Tx CLK
CLK POL
SRC
NORMAL
INVERTED
AUTO
CLOCK & DATA
DEMODULATION
RECOVERY
Theory of Operation
MODULATION
4-12
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